Processes of chemical nickel plating and baths therefor



2,999,770 PROCESSES OF CHEMICAL NICKEL PLATING 'AND RATES THEREFORGregoire Gutzeit, Highland, Ind., assignor to General AmericanTransportation Corporation, Chicago, 111., a New York corporation NoDrawing. Filed Aug. 27, 1953, Ser. No. 376,977 31 Claims. (Cl. 117-130)The present invention relates to improved processes of chemical nickelplating of catalytic materials employing baths of the nickelcation-hypophosphite anion type and to improved baths therefor; and theinvention is an improvement upon that disclosed in the copendingapplication of Gregoire Gutzeit and Abraham Krieg, Serial No. 194,656,filed November 8, 1950, now Patent No. 2,658,841, granted November 10,1953.

The chemical nickel plating of a catalytic material employing an aqueousbath of the nickel cation-hypophosphite anion type is based upon thecatalytic reduction of nickel cations to metallic nickel and thecorresponding oxidation of hypophosphite anions to phosphite anions withthe evolution of hydrogen gas at the catalytic surface. The reactionstake place when the body of catalytic material is immersed in theplating bath, and the exterior surface of the body of catalytic materialis coated with nickel. The following elements are catalytic for theoxidation of hypophosphite anions and thus may be directly nickelplated; iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium and platinum. The following elements are examples of materialswhich may be nickel plated by virtue of the initial displacementdeposition of nickel thereon either directly or through a galvanicefiect: copper, silver, gold, beryllium, germanium, aluminum, carbon,vanadium, molybdenum, tungsten, chromium, selenium, titanium anduranium. The following elements are examples of non-catalytic materialswhich ordinarily may not be nickel plated: bismuth, cadmium, tin, leadand zinc. The activity of the catalytic materials varies considerably;and the following elements are particularly good catalysts in thechemical nickel plating bath: iron, cobalt, nickel and palladium. Thechemical nickel plating process is autocatalytic since both the origi--nal surface of the body being plated and the nickel metal that isdeposited on the surface thereof are catalytic; and the reduction of thenickel cations to metallic nickel in the plating bath proceeds until allof the nickel cations have been reduced to metallic nickel, in thepresence of an excess of hypophosphite anions, or until all of thehypophosphite anions have been oxidized to phosphite anions, in thepresence of an excess of nickel cations. Actually the reactions areslowed-down rather rapidly as time proceeds because the anions, ascontrasted with the cations, of the nickel salt that is dissolved in theplating bath combine with the hydrogen cations to form an acid, which,in turn, lowers the pH of the bath, and the reducing power of thehypophosphite anions is decreased as the pH value of the bath decreases.Moreover, there is a tendency for the early formation in the platingbath of a black pre cipitate that comprises a random chemical reductionof the nickel cations. Of course, this formation of the blackprecipitate comprises a decomposition of the plating bath, and isparticularly objectionable in that it causes the nickel deposit to becoarse, rough and frequently porous.

For the dual purposes of retarding the formation of the blackprecipitate mentioned and of increasing the normal plating rate of thebath, various baths of the present type have been suggested employingdifferent additives. For example, in the previously-mentioned Gutzeitand Krieg patent, there is disclosed a chemical nickel plating bath ofthis type that contains, as an additive, a

buffer in the form of a soluble salt of an organic acid,

n e States at n 2,999,770 .Patented Sept. 12, 1961 of the bath beingwithin the approximate range 4.5 to 5.6,

the absolute concentration of hypophosphite ions in the bath being inthe range 0.15 to 0.35 mole/liter, the ratio between nickel ions andhypophosphite ions in the bath being in the range 0.25 to 0.60, and theabsolute concentration of acetate ions in the bath being approximately0.120 mole/liter.

In carrying out the chemical nickel plating process on a commercialscale employing a plating bath of the type mentioned, there may beutilized a continuous system of the character of that disclosed in thecopending application of Paul Talmey and William I. Crehan, Serial No.222,222, filed April 21, 1951, now Patent No. 2,658,839, grantedNovember 10, 1953; which system involves periodic or continuousregeneration of the plating bath by the addition thereto of appropriateingredients for the purpose of maintaining substantially constant thecomposition of the bath. More specifically in this system, there areprovided a plating chamber and a reservoir; one portion of the platingsolution is stored at a relatively low tempera-- ture well below theboiling point thereof in the reservoir; and another portion of theplating solution is held as a bath at a relatively high temperatureslightly below the boiling point thereof in the plating chamber. Thesolution is continuously circulated at alow rate from the reservoir tothe plating chamber and then back to the reservoir, the solution beingheated substantially to the relatively high temperature after withdrawalthereof from the reservoir and before introduction thereof into theplating chamber, and the solution being cooled substantially to therelatively low temperature after withdrawal thereof from the platingchamber and before return thereof to the reservoir. The body that is tobe nickel plated is immersed in the bath in the plating chamber, and issubsequently withdrawn from the bath in the plating chamber after a timeinterval corresponding to the thickness of the nickel plating thereonthat is desired; and during the time interval soluble reagents are addedto the solution in the reservoir to maintain in the bath in the platingchamber during the time interval substantially the predeterminedcomposition of the bath previously mentioned, so as to compensate forthe ingredients of the bath that are exhausted during the time intervalin the plating chamber; this regeneration of the solution in thereservoir consisting essentially of adding thereto appro priate amountsof soluble nickel-containing and hypophosbath having an optimum pH aslow as that mentioned is not always desirable.

The present invention is predicated upon the discovery that in platingbaths of the nickel cation-hypophosphite anion type mentioned, theformation of black precipitate may be retarded and the plating ratesthereof may be substantially increased by the addition thereto of a compound selected from the group consisting of short chain aliphaticamino'carboxylic acids and the salts thereof; which compounds functionto produce an exaltation phenomenon. Moreover, in the baththesecompounds are amphoteric, producing zwitterions, and therebyforming stable, water-soluble chelate complexes with nickel so that theuseful pH range of the bath can be substantially extended to embrace theneutral and near alkaline regions, without resulting in precipitation ofin soluble basic nickel salts. Further, these compounds are stable atelevated temperatures, i.e. near the boiling point of the plating bath,so that no reagent loss occurs in the neutral and alkaline zones wherepurer deposits are obtained. Finally, these compounds, by formingstable, water-soluble chelate complexes with the nickel ions, retardprecipitation of nickel phosphite, which is the normal by-product of thechemical nickel plating process resulting from the oxidation of thehypophosphite anions. The last-mentioned feature is particularlyimportant in continuous nickel plating operation in a system of thecharacter disclosed in the Talmey and Crehan patent in view of the factthat in such a continuous system the phosphite anion concentration soonbuilds-up, after a number of cycles, to a point where the solubility ofnickel phosphite is exceeded, with the resultant formation of nickelphosphite as a precipitate, and the consequent rough nickel plating.

In order to be of utility for the present purpose, the compoundsmentioned must, of course, be water-soluble; and moreover, for thepurpose of chelate formation with the nickel ions the amino group shouldbe either in the alpha or beta position with relation to the carboxylgroup, so that either fiveor six-membered rings will result.

Specifically, the zwitterions of the general formula Nun should have thespecific structures:

RR-RL-C 0 o m-a -o 0 oso that the resulting nickel chelates have thespecific structures:

0 o n-ii-o o :-n 11,1 1 16: --I\IH2 o n -n -ii-o o-ii-ru-m Hu -Ni "NH;

The hydrogen atoms of the amino group can, of course, be substituted, asthe nitrogen atom alone is necessary for ring closure. Water-solublesalts of amino acids, alpha or beta-polyamino acids,monoaminopolycarboxylic acids and polyaminopolycarboxylic acids aresuitable for the purpose. In other words, the watersoluble compoundsshould have the reactive groups:

1 It is noted that the chelate complexes (also called inner complexes)are particularly stable since all primary valences as well as thesecondary valences of the bound metal atom are satisfied. While, in anordinary inorganic cation complex, the coordinated molecules 4 form afirst zone around the central cation, which then becomes a new complexion, this is not the case in chelates; rather in chelates the wholestructure represents a new, very slightly dissociated, neutral molecule.A comparison between an ammonia complex of nickel and an amino-acidcomplex of nickel immediately shows this difference:

In view of the foregoing, it is the primary object of the presentinvention to provide an improved nickel plating process of the characterdescribed in which the reactions involved are carried out moreefliciently and under more stable conditions than heretofor, therebyrendering the process more desirable from a commercial standpoint.

Another object of the invention is to provide an improved aqueouschemical nickel plating bath which may be employed with advantage in thepractice of the improved process.

Another object of the invention is to provide an improved nickel platingprocess of the character described that employs a plating bath of thenickel cation-hypophosphate anion type containing as an exaltant acompound selected from the group consisting of short chain aliphaticaminocarboxylic acids and salts thereof.

A still further object of the invention is to provide an improvedaqueous nickel plating bath of the character described that containsnickel ions, hypophosphite ions and zwitterions.

These and other objects and advantages of the invention pertain to theparticular arrangement of the steps of the method and of the compositionof the plating bath, and will be understood from the foregoing andfollowing description.

In accordance with the process of the present invention, the article tobe nickel plated and normally having a catalytic surface is properlyprepared by mechanically cleaning, degreasing and light pickling,substantially in accordance with standard practices in electroplatingprocesses. For example, in the nickel plating of a steel object, it iscustomary mechanically to clean the rust and mill scale from the object,to degrease the object, and then lightly to pickle the object in asuitable acid, such as hydrochloric acid. The article is then immersedin a suitable volume of the bath containing the proper proportions ofnickel cations, hypophosphite anions and amino acid anions, the pH ofthe bath having been, if necessary, adjusted to an optimum value by theaddition of an appropriate 'acid or base, and the bath having beenheated to a temperature, just below its boiling point, such as 99 C. atatmospheric pressure. Almost immediately hydrogen bubbles are formed onthe catalytic surface of the steel object and, escape in a steady streamfrom the bath while the surface of the steel object is slowly coatedwith metallic nickel (containing some phosphorous). The reaction iscontinued until the color of the bath (green at the start) shows theabsence of nickel, or until the evolution of hydrogen gas stops, oruntil it is determined that the required thickness of the nickel coatinghas been deposited on the steel object. Of course the steel object isthen removed from the bath and rinsed off with water, and, is then readyfor use.

Instead of using a batch plating process, as described above, the steelobject may be plated in the plating chamber of the continuous system,previously described, by the immersion thereof in the plating chamberfor an appropriate time interval. Thereafter, the steel object isremoved from the plating chamber, and is rinsed oil with water and, isthen ready for use.

With, respect to the composition of the bath, it essentially comprisesan aqueous solution containing; nickel binations thereof; and thezwitterions may be derived from a compound selected from the groupconsisting of short chain aliphatic'aminocarboxylic acids and the saltsthereof. Specifically, a suitable bath may be formed in an exceedinglysimple manner by. dissolving in Water, nickel chloride, sodiumhypophosphite and sodium aminoacetate. The desired pH of the bath isestablished by the eventual introduction thereinto 'of hydrochloric acidor by the additionthereto of bicarbonate.

The terms cation, anion and ion, as employed herein, except wherespecifically noted, include the total quantity of the correspondingelements that are present in the plating bath, i.e. both undissociatedand dissociated material. In other words, 100% dissociation isassumedwhen the terms noted are used in connection with molar ratios andconcentrations in the plating bath, Also hereinafter the expressionpercent exaltation is employed with the arbitrary definition as thepercent increase in the rate of hydrogen evolution with reference to agiven Aminosuccinic acid Iminodiacetic acid CHz-C 0 0H 1'lI OH2OOOHIminotriacetic acid CHECOOH N-CHz-COOH I v our-coonEthylenediaminotetraacetic acid orb-coon HgCN v OHr-COOH e Y one-coonHaC-N oHPoooH As a matter of convenience, the zwitterions may beintroduced into the plating bath by dissolving therein, the salts,particularly the} alkali salts, of the short chain aliphatic'aminocarboxylic acids mentioned. Ihisis partic:

a weak alkali, preferably sodium ularl'yconvenient, since the alkalisalts of? these amino carboxylic acids are usually more readilyobtainable For example, the tetrasodium salt of.

upon the market. ethylenediaminotetraacetic acid is available in themarket under the various trade names: Versene," Nullapon, andSequestrene.

For the purpose of studying the increase of the hydrohypophosphite at aconcentration of 0.225 mole/liter (to which a trace of a nickel salt,i.e. 0.024 mole/liter was added to initiate the reaction at a vigorousrate).

Pickled pieces of mild steel, 20 cm. in area, were introduced forperiods of 30 minutes each. The different test solutions respectivelycontained no additive, and

additives in the form of salts of the following acids: acetic, citric,lactic, succinic, aminoacetic and aspartic. Specifically, the additives,when used, were employed as the sodium salts of the corresponding acidsin a con-- centration of 0.125 mole/liter of the anion, and the hydrogengas evolved was collected and its volume measured by usual methods. Theresults of these exaltation tests were:

H2 evolved in 30 min. from Additive (anion) 0.125 111/1. 50 cc. solutionPercent at 0.225 m/l. exaltation sodium hypophosphlte By comparison ofthe unsubstituted, and the aminosubstituted carboxylic acids, it will beobserved that a remarkable increase in percentage exaltation is producedby the substitution in the organic radical of one amino group for onehydrogen atom. Specifically, the exaltation figure for acetic anion is94; Whereas that for aminoacetic anion is 125 (a positive difference of31). Similarly, the exaltation figure for succinic anion is 175; Whereasthat for monoarninosuccinic anion (dl-aspartic) is 213 (a positivedifference of 38). Thehydroxy-substituted acids are in this connectioninferior to the unsubstituted carboxylic acids. [In conjunction withthese tests, it is noted that exaltation is independent of butteringefficiency and of the capability of the organic compound' to complex thenickel ions With the formation of chelates. In other words, the shortchain aliphatic aminooarboxylic acids, and the salts thereof, have thethree unrelated properties of exalt-ating, buffering and chelating; allof which are highly advantageous in the nickel. plating process.

In the use of short chain aliphatic aminocarboxylic acids for chemicalnickel plating exaltation, it is believed that this phenomenon resultsfrom the formation of a heteropoly-acid between the organic additive andthe hypophosphite anions, which competes with inner-com plex (chelate)formation between the nickel ions and the amino-acid radical. If thenickel amino-acid chelate istoo stable, insuflicient nickel cations areavailable for deposition, and the plating rate becomes low despite theexalting effect produced by the organic additive. In actual platingtests employing plating baths containing short chain aliphaticaminocarboxylic acids and watersoluble' salts thereof, it has been foundthat the pH variations have less influence on plating rates, in theoptimum nickel and hypophosphite ion concentration ranges, than is thecase with other organic additives. This is unquestionably due to theamphoteric character of the zwitterions. For example, with aminoaceticions (glycine) there are three optimum, although not particularlymarked, pH regions, i.e. at about 5.5, 6.5 and 8.5; and in any case, theuseful pH range of the plating bath is clearly extended with referenceto plating baths buttered with salts of simple, unsubstituted carboxylicacids of the character disclosed in the previouslyment-ioned Gutzeit andKrieg patent.

"On the other hand, in the case of short chain aliphatic amino-acidsalts (as opposed to ordinary buffers) added to the plating both, bestplating results are obtained when the ratio between the amino group andthe nickel ion is above 1.5; in other words, when the amount of aminoacid ions is suflicient to complex most or substantially all of thenickel ions contained in the plating bath. In this connection, it ispointed out that substantial exaltation is achieved in the plating bathwhen the amount of amino radical is such that the ratio mentioned isabove about 0.5 and that substantially all of the nickel ions arecomplexed to form chelates when the amount of amino radical is such thatthe ratio mentioned is 2 or above.

Again referring to the composition of the aqueous plating bath, thefollowing concentrations of ingredients have been found to be optimum:the absolute hypophosphite ion concentration should be in the range0.15. to. 1.20 mole/liter; the nickel ion/hypophosphite anion ratioshould be in the range 0.25 to 1.60; the ratio between the amino groupand the nickel ions should be in the range 0.5 to 6.0; and the pH shouldbe in the approximate range 4.5 to 9.0.

The exalting and other characteristics of the various In 50 cc. of thisplating bath, properly cleaned steel samples of 5 cm. area (16 gauge)were plated for 60 minutes, the temperature of the bath being 97 C.-98C. and the pH having been adjusted with sodium bicarbonate, with thefollowing results induplicate tests:

tory in the near neutral and basic regions of the pH range.

In a third series of these plating tests, anamino; acetate bath wasemployed that had the following composition:

Sodium hypophosphite m./1.. 0.225 Nickel chloride -m./l 0.1125 Sodiumaminoacetate Variable Ratio: Ni++/hypo- 0.5

In 50 cc. of this plating bath properly cleaned steel samples of 20 cm.area were plated for 10 minutes, the temperature of the bath being 97C'.98 C. and the pH thereof having been adjusted with acetic acid and/or caustic soda. In this plating bath, the plating rate, without theaddition of aminoacetate at pH 6.4 was only 0.84 10- gnu/cmP/min. andwith the aminoacetate additive, the plating was bright and smooth. Thespecific results in these tests were as follows (averages of duplicatetests being given):

short chain aliphatic aminocarboxylic acids in the platv ing baths wereestablished by a series of plating tests that S di aminoacetate /1 )5were made employing a series of test plating baths of the R i A i /Ni++053 general character of thatpreviously described and as explained moreparticularly hereinafter. T t 1 2 3| In the various plating testsappearing hereinafter 40 as weights of nickel plating deposited arereported in gms., Initial H 6 01 6 49 6 m and Plating rates are usuallyreported in gm/cm-zlmins mam mfiik'i jjlljiiiZZZIIIIIIIZ 21.10 2191 it;although occasionally plating rates are reported in mils/- hour, i.e.0.00'l"/hour).

In a first series of these plating tests, an aminoecetate g f f i 7fifiiplating bath was employed that had the following coma mmo 1 position:

Test 1 2 3 Sodium hypophosphite m./l 0.225 Nickel chloride m./l 0.075 50Initial pH 6.00 6.78 7.02 Sodium aminoacetaw 1 1125 Plating rate, RXlO3. 66 3. 36 3.42 Ratio: Ni++/hypo- 0.33 Ratio: Amino/Ni Sodiumaminoacetate m./'l 0.18 Ratio: Amino/Ni 1.60

In 50 cc. of this plating bath properly cleaned steel samples of 20 cm.area were plated for 10 minutes, the temperature of the bath being 96c.-9s c. and the pH Test 1 2 3 4 thereof having been adjusted withsodium bicarbonate, Inml H 6 98 6 20 6 39 6 62 With the followingresults! Platihg rafezibz fd i::::::::::: 4144 4199 4:31 4139 WeightRate (1115/ The above plating tests illustrate that best plating ratesInitial pH iiifii fg ii hour) are obtained when the ratio of theamino-nickel ions. is

above about 1.50. 6.5 (as prepared) 0.0996 1.3 In a fourth series ofthese plating tests, an amino- (as adjusted) Q1030 65 acetate bath wasemployed that had the following com- In a second series of these platingtests, an amino acetate bath was employed that had the followingcomposition:

position Sodium hypophosphite m./l-.. 0.225 Nickel chloride rn./l 0.0675Sodium aminoacetate Variable Ratio: Ni++/hypo" 0.3

In 50 cc. ofthis plating bath, properly cleaned steel samples of 20 cm.area were. plated for 10. minutes,v the temperature of the; bathvsubstantially 96 C. and

the pI-L having been: adjusted with acetic acid and/or caustic soda. Inthese plating tests, the plating was bright v and smooth, and thespecific results were as follows: Test 1 2 3 4 1 Initial pH 5.92 6.356.65 0.90 Sodium amlnmpefafe m 00675 5 Final pH 2.90 2.88 2.73 231'Ratio: Amino/N1++ 1.0 Weight gain 0.1015 0.1090 0.1110 0.1186

T 1 2 3 4 Sodium aminoacetate m./1 0.1013v Ratio Amino/Ni++ 1.5 InitialpH 5. 92 e. as 6. 05 s. 90 Plating rate, RXlO 2.22 2. 225 2.18 2. 535

Test; 1 2 3 4 Sodium aminoacetate m./l 0.1013

Initial pH 6.0 6.29 Ratio. Ammo/N1 1.5 Final pH 3. 25 3' 49 v 0. 1698 0.1728 Test 1 2 3 4 Initial DH 6 0 6 29 6 60 6 94 Sodium aminoacetate m./l0.135 matingma;rig-:3:::::::::::::::: 3.22.5 3398 4:03 4322 Ram Ammo/NIHSodium aminoacetate m./l 0.135, Test 1 2 a 4 Ratio: Amino/Ni++ 2.0

Initial pH 6.0 s. 22 6. 5s 0. 9s inal pH 3.37 3.51 1.12 I 4.72 Test 1 23 4 Weight gain 0. 1871 0. 1950 0. 2114 v 0. 2141 25 iaifigga',1550:1333:13:11:33: 4. 18 21%? 2:33 213.? a seventh Senes thesePlang tests In both the third and fourth of plating tests, it will beobserved that when the Ni++/hypophosphite ion ratio is either 0.5 or0.3, increased plating rates are obtained with increased ratios ofamino/Ni:

In a fifth series of these plating tests an amino-acetate bath wasemployed that had the following composition:

Sodium hypophosphite m./l 0.225 Nickel chloride m./l 0.0675 Sodiumaminoacetate Variable Ratio: Ni++/hypo* 0.3

In 50 cc. of this plating bath properly cleaned steel samples of 20 cm.area were plated for 10 minutes, the

temperature of the bath being 97 C. (:1 C.) and the pH having beenadjusted with NaOH and HCl. In these plating tests, the plating wasbright and smooth. The

specific results in these tests Were as follows (averages of triplicatetests being given):

Ratio: Amino/Ni 2.0 3.0 4.0

Initial pH 6. 64 70 6. Final pH 5. 58 5. 82 5. Weight gain 0. 0907 00984 0. 10 Rate, RX10 4. 54 4. 65 5.

From the fifth series of plating tests, it will be observed that thegreatest weight gains were achieved with this:

plating bath when the amino/Ni++ ratio was 4.0.

In a sixth series of these plating tests, an aminoacetate bath wasemployed that had the following composition:

Sodium hypophosphite m./l 0.225 Nickel chloride m./l 0.0675 Sodiumaminoacetate Variable Ratio: Ni++/hypo' 0.3

acetate bath was employed that had the following com position: 7

Sodium hypophosphite ..m./l 0.225 Nickel chloride m./l 0.1125 Sodiumaminoacetate Variable Ratio: Ni++/hypo- 0.5

In 50 cc. of this plating bath, properly cleaned steel samples of 20 cm.area were plated for 60 minutes, the temperature of the bath beingsubstantially at 98 C. In these plating tests, the plating was brightand smooth and the specific results were as follows:

Fromthese sixth and seventh series of plating tests, it will be observedthat over the time interval of 60 minutes, the weight gains of platingincrease with increasing pH and with increasing aminoacetateconcentrations. I

From this seventh series of plating tests, it will be observed that theweight gains in plating increase rapidly up to an aminoacetateconcentration of 0.18 mole/liter, and from thereon, at a much slowerrate. Moreover, it will be observed that the differences between theinitial and final pH values become smaller as the aminoacetateconcentration is increased due to buffering action in the bath. 1

In an eighth series of these plating tests where the Ni++/hyporatio wasvaried, an aminoacetate bath was employed that had the followingcomposition:

Sodium hypophosphite ..m./l 0.225. Nickel chlorid Variable Sodiumaminoacetate m./l 0.12

Sodium aminoacetate m./l.. 0.0675

Ratio: Amino/Ni++ 1.0

In 50 cc. of this plating bath, properly cleaned steel samples of 20 cm.area were plated for 10 minutes and 60 minutes, the temperature of thebath being substantially at 98 C. and the pH having been adjusted'witliammonium hydroxideto an initial valuewithin-the rangel 11 6.4 to 6.6. Inthese plating tests, the plating was bright and smooth and the specificresults were as follows:

10 MINUTE TESTS plating solution in the reservoir in excess of 24 cycles(as contrasted with a few cycles of regeneration employing prior bathsof the character of that disclosed in the Gutzeit and Krieg patent)before there is an intolerable Nwfhypv n o 128 0. 26 0.36 M12 575 Q 647build-up in the plating bath of the by-product phosph te. As a matter ofinterest, the plating rate of the plating N101, m./l 0.0288 0.0585 0.0310 0.1152 0.1293 0.1450 bath Subsequent cycle? the commuous PlatingFlnalpH 5.35 5.42 4.94 5.00 4 gg 485 system is increased over theinitial cycles thereof; which Rate, 3- phenomenon is not exactlyunderstood.

in In the continuous plating system, a plating bath was Ni++ h o- 0.7050.709 1.020 1. 232 1.538 emp oyed having the following composition: N'Cl/l 0 1580 0 1730 0 2303 0 2834 0 3400 Sodium hypophosphite" n""" 0225 12-111. 4.80 472 4.32 417 Nickel chloride m-./l 01125 Rate, 8X10 5. 424.80 4.29 a. 99 4. 08 Sodium aminoacetate m./l 0.225 Ratio: Ni++lhypo-0.5 MINUTE T STS Ratio: Amino/NH+ 2.20 60 E Trace ion stabilizer Pb++p.p.n1 1 Initial pH adjusted with 0.18 m./ l. NaOI-I 6.5 N1++/hyp0-0.128 0.20 0.30 0.512 0.575 0. 047

The trace of Pb++ was added to the plating bath to Fin-MPH: 504 337 18317 3,17 2,90 increase the stability thereof as disclosed in the previ-Weight gau1 0.0914 0.1702 0.1890 0.2282 0.2317 0.2300 ously mentionedTalmey and Gutzeit application In the continuous plating system, 6liters of the plating NiH/h 0 7o5 [L769 Q1026 0, 232 0,1533 bath wereused, the plating SOlutiOn being flOW'ed' by gravity through a heatingcoil and then through the Final H. 3.08 3.12 2.95 2. 2.88 platingchamber having a capacity of about 300 cm. so weight gm M234 051912 M055@2031 0-2113 that the temperature of the plating bath in the plating Ichamber was maintained at 99 C. (:L-l" C.). The plat- Th1s e1ghth seriesof plating tests shows that there is ing solution was regenerated in thereservoir exteriorly defimte Optlmum Tatlo 0f N1++/ yp p p 10118 111 30of the plating chamber after each cycle by adding thereto plating bathsdue to the inclusion in the commercial the necessary r -age t and foursteel samples of 20 reagents employed in the production of the platingbath cm. area each (80 cm. total area) were plated in the of stabilizingimpurities (particularly lead) with the con plating chamber with thefollowing results:

Cycle N0 1 2 3 4 5 6 7 8 Initial pH 0. 02 0. 02 0. 00 0. 4s 0. 57 0. 500. 51 0. 50 Final pH 0.22 0.19 0.29 0.15 0.10 0.29 0. 23 Duration nnn)115 90 100 39 93 204 101 100 Soln. flow rate co./min- 49 63 57 64 58 2256 54 Weight gain (gms.) 3. 80 2. 51 3. 34 2. 81 3. 00 3. 57 7. 00 4 10Plating rate, RX10 4. 13 3. 49 4. 17 3. 95 3.90 4. 52 4. 91 4 80Depletion percent 9.0 6.0 7.9 6.7 7.7 18.0 8.7 9.9 Cumulative deplet.percent 9.0 15. 0 22. 9 29. 6 37. 3 55. 3 611 0 73. 9

Cycle No 9 10 11 12 13 14 15 10 Initial pH 0. 0. 0; 49 0. 51 0. 49 0. 480. 4s 0. 47 Final pH 0. 01 0. 19 0. 31 0. 31 0. 35 0. 32 0. 30 0. 14Duration (min) 120 114 110 110 90 103 100 147 S0111. flow rate cit/min-45 49 52 57 54 39 Weight gain (gms.) 4 83 4. 52 4. 09 4. 52 4. 22 4. 504. 87 0. Plating rate, 13x10- 4.80 4. 5. 05 5. 14 5. 21 5. 54 5. 75 5.74 Depletion percent 11. 5 10. 7 11. 7 10. 7 10. 1 10.7 11. 6 16.0Cumulative deplet. percent 85. 4 96.1 107. 2 117. 9 128.0 138.7 150.3166.3

Cycle N0 17 18 19 20 21 22 23 24 Initial pH 0.49 0.50 0. 4a 0.45 0.520.40 0. 52 0. 52 Final pH 0. 23 0. 25 0. 32 0. 33 0. 32 0. 35 0. 30 0.42 Duration (min 130 141 102 130 145 128 S0111 flow rate so /m1n 42 4035 42 48 39 42 44 Weight; gain (gms.) 0. 24 0. 58 7.14 7 41 5. 87 7. 500. 05 0. 55 Plating.rate,R 10 5.73 5. 53 5.70 0.81 0.17 0. 45 0.22 0.40Depletion percent 14.8 15.0 10. 9 Y 17.0 13.9 17.7 15.8 10.5 Cumulativedeplet. percent- 181.1 190. 7 213. 0 231. 2 245.1 202. 8 278. 0 295.1

sequent inclusion in the bath of a trace of amount of sulfide ioncontroller as disclosed in the copending application of Paul Talmey andGregoire Gutzeit, Serial No. 359,428, filed June 3, 1953. Specifically,the optimum ratio of N-i++/hypophosphite ions in plating bathscontaining amino-acids is between 0.575 and 0.650, due to thecircumstance noted.

In the foregoing series of plating tests, a batch plating process wasinvolved; however, baths of the present type are even more advantageouswhen employed in a continuous plating system as disclosed in the Talmeyand Crehan patent. Specifically,.thesebaths have a fast plating rate amtare stable: permitting; regeneration of the- This test was stopped after24 cycles without reaching the point where nickel phosphite precipitatedin the plating solution, whereby a total weight of 123.81 gms. of nickelwas plated from the 6 liters of plating solution without phosphiteremoval, the volume of the plating solution being kept constant byadding some water as the rate of evaporation was greater than the volumeof reagent solution added for regeneration. The percent of depletion isan arbitrary indication of the amount of nickel taken out, as a deposit,from the original solution.

In these plating baths, the nickel ion may be supplied by nickel saltsother than the chloride, such, for instance, as the sulfate; and in thefollowing plating tests employgenome 13 ing the continuous platingsystem, the'following plating bath composition was used:

In the plating system, the conditions were the same as previouslydescribed with reference to the preceding plating test and the followingresults were obtained:

Cycle No l 2 3 4 5 Initial pH 6. 38 6. 49 6. 54 6. 48 6.50 Final H--5.96 6.19 6. 20 6. 07 6. 27 Duration (mm.) 117 97 115 155 114 Soln. flowrate cc./m 49 59 49 37 50 Weight gain 4. 66 3. 51 4.05 5. 39 4.14Plating rate, RXlOt 4. 98 4. 53 4. 40 4. 34 4. 53 Depletion percent 11.18.3 9. 6 12. 8 9.8 Cumulative depl. percent 11. 1 19. 4 29. 41. 8 51. 6

Cycle No 6 7 8 9 10 In all of the foregoing plating tests, steel wasused as the plating base material; however, it should be understood thatother materials, such as, aluminum, brass, bronze, plastic (Bakelite),etc., may be plated with very good results using these plating baths. Inthe plating of aluminum bodies a bath of the general character of thatdisclosed in the copending application of Raymond R. Reschan and AbrahamKrieg, Serial No. 309,939, filed September 16, 1952, now Patent No.2,694,017, granted November 9, 1954, is recommended and a plating bathof this character was used in plating tests and havingthe followingcomposition:

In 50 cc. of this plating bath a sample of steel and a sample of 28aluminum each of 20 cm? area were separately plated for 11 minutes at atemperature of about 98 C., with the following results:

Base material Steel 28 aluminum Initial pH 6. 41 6. 41 Weight gain 0.0920. 128 Plating rate, R 4. 26 6. 82

The plating on the S2 aluminum sample showed excellent adhesion; andthese results were verified in a companion 60 minutes test.

In other plating tests a bath of the general character of that disclosedin the Reschan and Krieg patent was employed that had the followingcomposition: 7

Sodium hypophosphite m./l 0.225 Nickel chloride m./l 0.1125 Sodiumaminoacetate m./l 0.18 Sodium fluoride m./l' '0.01

Sodium nitrate m./l 0.20 Initial pH, adjusted with NaOH 6.5 Ratio:Ni++/hypo 0.5 Ratio: Amino/Ni 1.6

In 50 cc. of this plating bath a sample of steel and'a' sample of S2aluminum each of 20 cm? area were separately plated for 10 minutes, thetemperature of the bath being about 98 C., with the following results:

Base material Steel Aluminum Weight gain 0.0969 0.0984. Rate, R 10 4.855.29. Appearance Bright, smooth... Very bright, smooth. Adhesion GoodExcellent.

In another plating test three brass faucets were plated to 0.4 milthickness in a bath having the following composition:

In this plating bath the plating rate was 1 mil per 50 minutes and theappearance of the faucets after plating was unusually good.

In another plating test, a sample of general purpose Bakelite was platedin a bath having the following composition:

Sodium hypophosphite m./l 0.225

Nickel chloride m./l 0.1125 Sodium aminoacetate m./l 0.18 Pb++ added asstabilizing ion p.p.m 5

Prior to plating, the sample of Bakelite was prepared in accordance withthe methods disclosed in the copending applications of Gregoire Gutzeit,William J. Graham and Abraham Krieg, Serial No. 230,352,'filed June 7,1951, now Patent No. 2,690,401, granted September 28, 1954, and ofWilliam J. Crehan, Serial No. 279,945, filed April 1, 1952, now PatentNo. 2,690,402, granted September 28, 1954. Specifically, the outer layerof skin of the Bakelite sample was removed mechanically with fine emerycloth; and then it was soaked in an aqueous solution containing 35 ppm.of palladium chloride for 72 hours. The sample was then thoroughlyrinsed in warm water, dried, and the palladium chloride was reduced tometallic palladium in a hot aqueous solution of sodium hypophosphite(0.335 m./l.) until bubbling subsided. The plating was initiatedinstantaneously upon immersion of the prepared Bakelite sample into theplating bath at a temperature of 92 C.; and the plating was carried outfor a time interval of minutes in 50 cc. of the plating bath. Theplating appearance was excellent and the adhesion thereof was good. Inthe plating test the bath remained stable and very clear.

In passing, it is noted that further plating tests showed that a soakingfor 3 hours in the aqueous palladium chloride solution is optimum forcoating adhesion although a soaking time as short as 5 minutes isadequate to obtain initiation of the nickel plating.

In succeeding plating tests, the same technique was applied in thepreparation of other plastic materials including fiberglass reinforcedpolyester plastic, neoprene and phenolic plastic ,(Hycar). These platingtests were also highly successful in that the plating appearance wasexcellent and the adhesion was good.

Aplating test ..upon a. fBa-kelite sample was 0.0.11-

'15 ducted employing the continuous plating system previously describedand utilizing a plating bath having the following composition:

Sodium hypo-phosphite 'm./l 0.225 Nickel sulfate m./l 0.1125 Sodiumaminoacetate m./l 0.2.25 Ratio: Ni++/hypo* 0.5 Ratio: Amino/Ni++ 2.0Stabilizing ion Pb++ p.p.m 4 Initial pH adjusted with NaOH 6.406.50

In this plating test, the bath had a volume of 4.5 liters and theBakelite sample was pretreated substantially in the manner previouslydescribed. Specifically, the pretreatment of the Bakelite sampleconsisted of the removal of the skin thereon on a sanding belt, followedby the soaking thereof for about 15 minutes in an aqueous solution ofpalladium chloride (35 ppm.) at a temperature in the range 60 C.80 C.Thereafter the Bakelite sample was rinsed in hot Water, and then 1 6 Inanother series of these plating tests, an alpha-- alanine plating bathwas employed that had the following composition:

1 Sodium hypophosphite m./l 0.225 Nickel chloride rn./l 0.1125Alpha-alanine m./l 0.225 Radio: Ni++/hypo* 0.5 Ratio: Amino/Ni++ 2.0 pH,adjusted with NaOH Variable In 50 cc. of this plating bath, properlycleaned steel samples of 20 cm. area were plated, the temperature of thebath being about 97 C. In these plating tests, the plating was brightand smooth in the acid bath, semibright in the substantially neutralbaths, and dull in the alkaline baths, and the specific results were asfollows:

(a) Rate tests-40 minutes immersed in a hot aqueous solution of sodiumhypoy Initial H 5.54 0.01 0.52 7.01 7.53 7.00 8.53 9.00 phosphlte 0.225111-! 11ml bubbhllg SUbSGded' Them wei ht gam 0.0000 0. 0923 0. 0802 0.0789 0. 0847 0.0802 0. 0839 0. 0251 after the Bakelite sample was rinsedin hot water Rate, RXlO 3. 48 4. 4.31 3. 4 4424 4.01 4.40 4.10 andtransferred to the plating chamber in the continuous plating system;whereby it was plated therein with (b) Plating tests-60 minutes thefollowing results:

. rninai rr 5.54 0.01 0.52 7.01 7. 53 7.99 7.53 9.00 Gym N0 1 2 3 5 6 7Weightgam 0. 2045 0.2373 0.2544 0.2558 0.2595 0. 2325 0. 2252 0.2044

lnitialpH 0. 44 0.51 0.50 0.47 0.45 0. 48 0.47 In a series of theseplating tests, a beta-alanine (dlggf i gq 6:35 beta-aminopropionic acid)plating bath was employed cc./m1'.n 38 40 38 37 43 40 43 that had thefollowing composition: Weightgain, gins... 3. 7475 3.4501 3. 2524 4.10703.0540 3. 9210 4.7550 Cumulative depleti0n,percent 12.6 24.2 35.2 49.263.0 76.4 91-6 Sodium hypophosphite Il1./l 0.225 Nickel chloride m./l0.1125 In the foregoing series of plating tests, the short chainBeta-alanine m./l 0.225 aliphatic arninocarboxylic acid additive in theplating Radio: Ni++/hypo- 0.5 bath consisted of aminoacetic acid(glycine) or the alkali Ratio: Amino/Ni++ 2.0

salt thereof, fundamentally due to the practical circumstance that thesecompounds are both cheap and readily avail-able in large quantities inthe commercial market. Moreover, it has been verified that the othershort chain aliphatic aminocarboxylic acids do not have any particularadvantage over glycine and they are considerably more expensive and onlyavailable in small quantities in the market. Accordingly, [from apractical standpoint, it is recommended that the short chain aliphaticaminocarboxylic acid additive in the plating bath take the form ofglycine or sodium aminoacetate. However, the other short chain aliphaticaminocarboxylic acids and their salts are entirely satisfactory asadditives in the plating bath as indicated by the various series ofplating tests reported hereinafter.

In a series of these plating tests, an alpha-alanine(dialpha-aminopropionic acid) plating bath was employed that had thefollowing composition:

In 50 cc. of this plating bath, properly cleaned steel samples of 20 cm.area were plated, the temperature of the bath being 97 C.i1 C. In theseplating tests, the plating was bright and smooth and the specificresults were as follows:

Duration of test 10 minutes 60 minutes Initial pI-I 6.10 6. 10 FinalpH... 5.10 8. 10 Weight gain. 0. 1050 0. 2231 Rate, 11x10 5. 25

Initial pH adjusted with NaOH.

In 50 cc; of this plating bath, properly cleaned steel samples of 20 cm.area were plated, the temperature of the bath being 97 C.J -l C. Inthese plating tests, the plating was bright and smooth, and the specificresults were as follows:

Duration of test 10 minutes 60 minutes Initial pH 6; 05 7. 68 8. 61 6.7. 58 8. 61 Weight gain 0. 0523 0.0727 0.0820 0. 1294 0. 1378 0. 1639Rate, RXlO- 2. 01 3. 64 4.10

Sodium hypophosphite m./l 0.225 Nickel chloride m./l 0.09Alphaeminobutyric acid m./l 0.18 Ratio: Ni+'+/hypo 0.4 Ratio: Amino/Ni2.0 Initial pH adjusted with NaOH 6.5

In 50 cc. of this plating bath, properly cleaned steel samples of 20 cm.area were plated, the temperature of the bath being 97 C.:L1 C. In theseplating tests, the

17 plating was bright and smooth and the specific results were asfollows:

Duration of tests 10 minutes 60 minutes 6. 50 6. 50 Final pH 5. 80 3. 60Weight gain- 0. 0740 0. 2401 Rate, R 10 3. 70

In another series of these plating tests, an alpha-amino butyric acidplating bath was employed that had the following composition:

Sodium hypophosphite m./l 0.225 Nickel chloride m./l 0.1125Alpha-aminobutyric acid m./l 0.225 Radio: Ni++/hypo* 0.5 Ratio:Amino/Ni++ 2.0 pH adjusted with NaOH Variable In 50 cc. of this platingbath, properly cleaned steel samples of 20 cm? area were plated, thetemperature of the bath being about 97 C. In these plating tests, theplating was bright and smooth in the acid baths, dull in thesubstantially neutral baths, and semi-bright in the alkaline baths, andthe specific results were as follows:

(a) Rate testsl mlin'utes Initial pH 5.52 6.05 6.53 7.00 7.56 8.62 9.10

Weight gain 0.0733 0.0684 0.0533 0. 0480 0.0464 0.0608 0.0576

Rate, R 3.66 3.42 2.66 2.40 2.32 3.04 2.88

(b) Plating tests-60 minutes Initial pH 5.53 6.05 6.53 7.00 7. 56 8.088.62 9.10

Weight gain 0.1902 0. 2356 0. 2468 0. 2465 0. 2321 0. 2310 0. 2224 0.2000 In connection with the alpha-aminobutyric acid baths, it is pointedout that while the 10 minute rates are low, the '60 minute rates comparevery well with those obtained in the aminoacetic acid bath; whichcircumstance indicates a long initiation period, possibly due to thefact that a longer time is needed for reaching a complexationequilibrium.

In the continuous plating system, an aminosuccinic acid (aspartic acid)plating bath was employed having the In the plating system, theconditions were substantially the same as previously described withreference to the prior plating tests involving the continuous platingsystem, except that only 4 liters of the bath were employed and thetotal area of the steel samples was 6 0 cmfi, the temperature of thebath being about 99 C., and the following results were obtained:

Oycle No 1 2 3 7.00 6. 70 6. 6. 40 6. 20 6. 30 1. 4009 l. 1415 1. 56553. 31 3. 73 3. 89 Duration of cycle (min) 72 51 67 Soln. flow ratecc./min 51. 4 78. 4 59. 6

In this aspartic acid bath, the plating was bright and smooth.

In a series of these plating tests, an ethylenediamino tetraacetic acidplating bath was employedtha-t was 18 formed from the tetrasodium saltthereof (Versene) and that had the following composition:

Sodium hypophosphite m./l Nickel chloride m./lEthylenediaminotetraacetic acid (tetrasodium salt thereof) m /l 0.04Ratio: Ni++/hypo- 0.4 Ratio: Amino/Ni++ 0.9

Initial pH adjusted with acetic acid or NaOH.

In 50 cc. of this plating bath, properly cleaned steel samples of 5 cm.area (shimstock) were plated for 10 minutes, the temperature of the bathbeing 97 Oil C. In these plating tests, the plating was bright andsmooth and the specific results were as follows:

6. 0, 7. 0 8-. 0 Final pH 3. 5 3. 5 4. 9. Weight gain (gms.) 0. 0345 0.0367 0. 0679 In passing, it is noted that Versene is chemicallyidentical to Nullapon. and Sequestrene that have also been employed withidentical results. In these tests, the weight: gains should bemultiplied by four for comparison purposes with the other plating tests(because the area of the steel sample was 5 cm? instead of 20 cm? aspreviously) and it will be observed that this additive(ethylened'iaminotetraacetic acid) produces optimum results in' thealkaline range where this'complexing agent is most effetcive. a

In connection with Versene-Fe-Sp (an acid sodium salt ofethylenediaminotetraacetic acid), it is pointed out that the optimumresults are obtained in the near acid range R and the following bathcomposition is recommended:

Sodium hypophosphite 0.225 Nickel chloride 0.09 Versene-Fe-Sp 0.04

In 5 0 ccfof this plating bath, properly cleaned steelsamples of 5 cm?area (shimstock) were plated, the tem-' perature of the bath being 97 C.11 C. In these plating tests, the plating was bright and smooth and thespecific results were as follows:

Initial pH 5. 0 6. 0 Final pH 4. 3 4. 1 Weight gain (gms.) 0. 0458 0.0530 Again it is noted that in these plating tests the weight gainsshould be multiplied by four for comparison pur-.

poses with the other plating tests.

As previously noted, the utilization of an short chain aliphaticaminocarboxylic acid additive in a plating bath. of the character ofthat disclosed in the Gutzeit and Krieg patent is'advantageous and aplating bath of this character of the following compositionisrecommended:

Magnesium hypophospite 0. 15 6' m./l.

Nickel acetate 0.086 m./l. Versene (38% soln.) Variable (0.2% and 1%corresponding to about 0.0027 and 0.0135 m./l.).' Initial pH adjustedwith acetic acid 5.69

In 50 cc. of this plating bath, properly cleaned steel samples of 20 cm?werev plated for 60 minutes, the temperature of the bath being about 97C. and the following results were obtained:

Versene None 0.2% 1.0% None 1% Duration of test-min 1O 10 10 29 Weightgain 0. 1106 0.1168 0.1246 0. 2296 0. 2426 Stability (min) Stable StableStable 20 Stable 19 It is noted that this bath is an acetate bufferedbath and that the Versene additive results in increased plating rate andhas a stabilizing action at a concentration of 1% (0.0135 m./l.).

In passing, it is noted that in similar tests Bakelite samples, preparedin the manner previously explained, were plated, and it was found thatthe initiation period was shortened from about 9 minutes :to about 3minutes, again indicating the advantage of utilizing the short chainaliphatic aminocarboxylic acid additive in an acetate buffered bath ofthe character of that disclosed in the Gutzeit and Krieg patent.

In a further series of plating tests, several short chain aliphaticarninocarboxylic acid additives were employed in each bath, and it wasdiscovered that their actions were accumulative and good results wereobtained. In these plating tests, the following four baths were utilizedrespectively designed as I, II, III and IV, and having the receptivecompositions:

In 50 cc. of these plating baths, properly cleaned steel samples of 5cm. area were plated for 60 minutes, the temperature of the baths being98 C: 1 C., with the following results:

Bath No I II III IV Initial pH 5. 7s 6. 0 6. 0 6. 0 Final pH 5. 0 4. 34. 4 3. 8 Weight gam (gms) 0.1214 0.1563 0.1506 0.1584

In view of the foregoing, it is apparent that there has been provided animproved process of chemical nickel plating, as well as improved platingbaths therefor, wherein the baths are of the nickel cation-hypophosphiteanion type containing as an additive a compound selected from the groupconsisting of short chain aliphatic aminocarboxylic acids and saltsthereof. The additives mentioned are very advantageous in the platingbath in that they function both as exaltants and as to the plating rateand as retarders as to the formation of black precipitate. Moreover, inthe arrangement, the nickel plating may take place within a wide pHrange (from about 4.5 to about 9.0), being most useful aroundneutrality, Where the base metal is least attacked by the plating bathand where plating equipment corrosion is minimized. Furthermore, whenthese additives are used in the optimum proportion (am-ino/Ni about 2.0)they keep the nickel phosphite from precipitating after many cycles inthe continuous plating system, rendering it possible to reach aphosphite concentration of about 1 molar (instead of the usual 0.07m-./l.) before precipitation starts in the plating bath.

While there has been described what is at present considered to be thepreferred embodiment of the invention,

it will be understood that various modifications may be made therein,and it is intended to cover in the appended claims all suchmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A method of depositing nickel from a chemical reduction plating bath,said method comprising immersing a catalytic article to be coated in asolution of nickel ion and a hypophosphite reducing agent capable ofreducing the nickel in solution, said solution having a nickel ionconcentration of about 7 grams per liter, a hypophosphite ionconcentration of about 15 grams per liter, a relatively high platingtemperature that is disposed near the boiling point thereof, and aninitial pH Within the range from about 5.5 to 9.1, and allowing saidarticle to remain in said solution until a nickel coating of desiredthickness is deposited thereon.

2. A method of depositing nickel from a chemical reduction plating bath,said method comprising immersing a catalytic article to be coated in asolution of nickel ion and a hypophosphite reducing agent capable ofreducing the nickel in solution, said solution containing an initialquantity of nickel ion of about 7 grams per liter and an initialquantity of hypophosphite ion of about 15 grams per liter and having aninitial pH within the range from about 5.5 to 9.1, said solution havinga relatively high plating temperature that is disposed near the boilingpoint thereof, and allowing said article to remain in said s0lut-ion fora time interval sufiicien-t to reduce said initial quantity of nickelion therefrom.

3. The method set forth inclaim 2, and further comprising regeneratingsaid solution during said time interval by adding thereto solubleingredients supplying thereto nickel ion and hypophosphite ion andhydroxyl ion in order to maintain during said time interval in saidsolution substantially said initial quantity of nickel ion andsubstantially said initial quantity of hypophosphite ion andsubstantially said initial pH thereof, and so that the total reductionof nickel ion from said solution during said time interval is in excessof said initial quantity of nickel ion therein.

4. A method of depositing nickel from a chemical reduction plating bath,said method comprising immersing a catalytic article to be coated inasolution of nickel ion and a hypophosphite reducing agent capable ofreducing the nickel in solution, said solution having a nickel ionconcentration of about 7 grams per liter, a hypophosphite ionconcentration of about 15 grams per liter, a relatively high platingtemperature that is disposed near the boiling point thereof, and aninitial pH within the range from about 5.5 to 9.1, and allowing saidarticle to remain in said solution until the nickel is substantiallycompletely reduced as evidenced by the solution turning from green tocolorless.

5. A method of depositing nickel on a catalytic surface by chemicalreduction plating, said method comprising immersing the article to becoated in an aqueous solution of nickel acetate and an alkalinehypophosphite, the nickel ion concentration of said solution being about5 grams per liter and the hypophosphite ion concentration being about 10grams per liter, said solution having an initial pH within the range ofabout 5.5 to 9.1 and being maintained at a relatively high platingtemperature that is disposed near the boiling point thereof, andmaintaining said article in such solution for a time sufficient toreduce substantially all of the nickel in solution as evidenced by thesolution turning from green to colorless.

6. A method of depositing nickel from a chemical reduction platingsolution which comprises immersing the articles to be plated in anaqueous solution containing nickel ion, acetate ion and hypophosphiteion, and having an initial pH from about 5 .5 to 9.1, the nickel ionconcentration being about 5 grams per liter, the hypophosphite ionconcentration being about 10 grams per liter and the ratio of acetateion to nickel ion being about 2 to 1, maintaining said solution at arelatively high plating temperature that is disposed near the boilingpoint thereof, and allowing said articles to remain in said solution fora time suilicient to reduce substantially all the nickel in thesolution.

7. A method of depositing nickel from a chemical reduction platingsolution which comprises immersing the articles to be plated in anaqueous solution of nickel chloride, an alkali metal hypophosphite and asoluble acetate, and having an initial pH from about 5.5 to 9.1, thenickel ion concentration being about grams per liter, the hypophosphiteion concentration being about grams per liter and the acetate ion beingsufficient to exert a buffering action, maintaining said solution at arelatively high plating temperature that is disposed near the boilingpoint thereof, and allowing said articles to remain in said solution fora time suflicient to reduce substantially all the nickel in thesolution.

8. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum;which comprises contacting said body with an aqueous bath comprisingnickel ions and hypophosphite ions and a dissolved compound selectedfrom the group consisting of short chain aliphatic aminocarboxylic acidsand salts thereof, wherein the absolute concentration of hypophosphiteions in said bath expressed in mole/liter is within the range 0.15 to1.20, the molar ratio between nickel ions and hypophosphite ions in saidbath is the range 0.25 to 1.60, the numerical ratio between amino ionsand nickel ions in said bath is within the range 0.5 to 6.0, and theinitial pH of said bath is within the approximate range 4.5 to 9.0.

9. The process set forth in claim 8, wherein the'molecule of saidcompound comprises from 2. to 10 carbon atoms.

10. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of alphaaminocarboxylic acids and saltsthereof.

11. The process set forth in claim 10, wherein saidalpha-aminocarboxylic acid is alpha-aminopropionic acid.

12. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of beta-aminooarboxylic acids and saltsthereof.

13. The process set forth in claim 12, wherein said beta-aminocarboxylicacid is beta-aminopropionic acid.

14. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of polyaminocarboxylic acids and saltsthereof.

15. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of aminopolycarboxylic acids and saltsthereof.

16. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of polyaminopolycarboxylic acids and saltsthereof.

17. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of ethylene diaminotetraacetic acid and saltsthereof.

'18. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of aminoacetic acid and salts thereof.

19. The process set forth in claim 8, wherein said compound is selectedfrom the group consisting of aminosuccinic acid and salts thereof.

20. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palaldium and platinum;which comprises contacting said body with an aqueous bath comprisingnickel ions and hypophosphite ions and short chain aliphatic zwitterionsof the general formula:

where R is an al-klyl radical, wherein the absolute con centration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the molar ratio between nickel ions andhypophosphite ions in said bath is within the range 0.25 to 1.60, thenumerical ratio between zwitterions and nickel ions in said bath iswithin the range 0.5 to 6.0, and the initial pH of said bath is in theapproximate range 4.5 to 9.0.

21. The process set forth in claim 20, wherein the numerical ratiobetween zwitterions and nickel ions in said bath is at least 2 so thatsubstantially all of the nickel ions in said bath are chelated.

22. The process set forth in claim 20, wherein the resulting chelate isof the general structure:

H2111 --\-N'/ l where R is an alkyl radical.

23. The process set forth in claim 20, wherein the resulting chelate isof the general structure:

HzN- Ni "NH:

Where R and R are alkyl radicals.

24. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum;which comprises contacting said body with an aqueous bath comprisingnickel ions and hypophosphite ions and short chain aliphatic zwitterionsof the general formula:

NHa

where R and R are alkyl radicals, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the molar ratio between nickel ions andhypophosphite ions in said bath is within the range 0.25 to 1.60, thenumerical ratio between zwitterions and nickel ions in said bath iswithin the range 0.5 to 6.0, and the initial pH of said bath is in theapproximate range 4.5 to 9.0.

25. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum;which comprises contacting said body with an aqueous bath comprisingnickel ions and hypophosphite ions and short chain aliphatic zwitterionsof the general formula:

NHa' where R and R are alkyl radicals, wherein the absoluteconcentration of hypophosphite ions in said bath expressed in mole/literis within the range 0.15 to 1.20, the molar ratio between nickel ionsand hypophosphite ions in said bath is within the range 0.25 to 1.60,the numerical ratio between zwitterions and nickel ions in said bath iswithin the range 0.5 to 6.0, and the initial pH of said bath is in theapproximate range 4.5 to 9.0.

26. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum;which comprised contacting said body with an aqueous bath comprisingnickel ions and hypophosphite ions and a dissolved compound selectedfrom the group consisting of short chain aliphatic aminocarboxylic acidsand salts thereof, said bath having a hypophosphite ion concentration inthe range 10 to grams per liter, the molar ratio between nickel ions andhypophosphite ions in said bath being within the range 0.25 to 1.60, thenumerical ratio 23 between amino ions and nickel ions in said bath beingwithin the range 0.5 to 6.0, and the initial pH of said bath being inthe approximate range 4.5 to 9.0.

27. A bath for the chemical plating of a catalytic material with nickelcomprising an aqueous solution of a nickel salt and a hypophosphite anda compound selected from the group consisting of short chain aliphaticaminocarboxylic acids and salts thereof, wherein the absoluteconcentration of hypophosphite ions in said bath expressed in mole/literis within the range 0.15 to 1.20, the molar ratio between nickel ionsand hypophosphite ions in said bath is within the range 0.25 to 1.60,the numerical ratio between amino ions and nickel ions in said bath iswithin the range 0.5 to 6.0, and the pH of said solution is in theapproximate range 4.5 to 9.0.

28. A bath for the chemical plating of a catalytic material with nickelcomprising an aqueous solution of nickel ions and hypophosphite ions andshort chain aliphatic zwitterions of the general formula:

where R is an alkyl radical, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the molar ratio between nickel ions andhypophosphite ions in said bath is within the range 0.25 to 1.60, thenumerical ratio between zwitterions and nickel ions in said bath iswithin the range 0.5 to 6.0, and the pH of said bath is in theapproximate range 4.5 to 9.0.

29. The bath set forth in claim 28, wherein the numerical ratio betweenzwitterions and nickel ions is at least 2 so that substantially all ofthe nickel ions are chelated.

30. A bath for the chemical plating of a catalytic material with nickelcomprising an aqueous solution of a nickel salt and a hypophosphite anda compound selected from the group consisting of short chain aliphaticaminocarboxylic acids and salts thereof, said bath having ahypophosphite ion concentration in the range 10 to grams per liter, themolar ratio between nickel ions and the hypophosphite ions in said bathbeing within the range 0.25 to 1.60, the numerical ratio between aminoions and nickel ions in said bath being within the range 0.5 to 6.0, andthe pH of said bath being in the approximate range 4.5 to 9.0.

31. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum,which comprises contacting said body with an aqueous bath comprisingabout 0.15 to 1.20 moles per liter of hypophosphite ions, about .04-2moles per liter of nickel ions and about .02-l.5 moles per liter of asalt of ethylene diamine tetra acetic acid, said bath having a pH'ofabout 4.5-6.5.

References Cited in the file of this patent UNITED STATES PATENTSBrenner Dec. 5, 1950 2,658,839 Talmey et al. Nov. 16, 1953 2,658,841Gutzeit et a1. Nov. 10, 1953 2,721,814 Jendrzymski et al Oct. 25, 1955OTHER REFERENCES

1. A METHOD OF DEPOSITIONG NICKEL FROM CHEMICAL REDUCTION PLATING BATH,SAID METHOD COMPRISING IMMERSING A CATALYTIC ARTICLE TO BE COATED IN ASOLUTION OF NICKEL ION AND A HYPOPHOSPHITE REDUCING AGENT CAPABLE OFREDUCING THE NICKEL SOLUTION, SAID SOLUTION HAVING A NICKEL IONCONCENTRATION OF ABOUT 15 GRAMS PER LITER, A HYPOPHOSPHITE IONCONCENTRATION OF ABOUT 15 GRAMS PER LITER, A RELATIVELY HIGH PLATINGTEMPERATURE THAT IS DISPOSED NEAR THE BOILING POINT THEREOF, AND ANINITIAL PH WITHIN THE RANGE FROM ABOUT
 5. 5 TO 9.1, AND ALLOWING SAIDARTICLE TO REMAIN IN SAID SOLUTION UNTIL A NICKEL COATING OF DESIREDTHICKNESS IS DEPOSITED THEREON.